Inefficient processing of raw timber and lumber wastes tremendous forest resources. To that end, the forest products industry is always looking for the ability to effectively and economically match the lumber needs of end-users and the lumber supplier of the product. It is well known that many factors control the suitability of lumber for any particular purpose. One factor that has become an increasingly important consideration is warp stability of lumber. The presence of warp affects the grading of the lumber, and thus, the value of the lumber to the lumber supplier.
Currently known methods of predicting warp potential in wood products, such as lumber, are disclosed in U.S. Pat. Nos. 6,293,152, 6,305,224 and 6,308,571, the disclosures of which are hereby incorporated by reference. A brief discussion of one conventional method for determining warp potential in wood products will now be described with reference to FIG. 1, which illustrates a pictorial overview of such a warp potential determination method. Generally described, the warp potential determination method quantifies a lengthwise shrinkage map for a selected wood product and then quantifies the warp potential in such a wood product based on the lengthwise shrinkage map.
To quantify the lengthwise shrinkage map of the wood product, several steps typically occur. First, sound velocity measurements, which are a non-destructive way of obtaining stiffness measurements, are taken at a plurality of measuring locations along the wood product and compiled to form a sound velocity profile, as best shown in FIG. 1. One example of a sound velocity profile generated in this manner is shown in FIG. 2. The sound velocity measurements may be taken at any interval along the wood product's width and length. Next, an empirical relationship or correlation between actual lengthwise shrinkage and sound velocity for the wood product (i.e., loblolly pine lumber) is obtained. This correlation is typically obtained by conducting tests on a plurality of sample specimens that are representative of the wood product. For example, sound velocity measurements may be obtained for each specimen. Next, actual lengthwise shrinkage measurements of each specimen are obtained. This may be accomplished by measuring the specimens at an equilibrium moisture content (EMC) at a relative humidity (RH) of 90%. The specimens are then brought to an equilibrium moisture content at 20% RH and the lengthwise shrinkage measurements are repeated. After the sound velocity measurements and the actual lengthwise shrinkage measurements are obtained for each specimen, a correlation between sound velocity and lengthwise shrinkage may be determined using well-known regression techniques, such as the least squares model. One example of sound velocity-lengthwise shrinkage correlation generated in this manner is shown in FIG. 3.
Once the empirically determined, sound velocity-lengthwise shrinkage correlation is quantified, the resulting quantified correlation is utilized to convert the sound velocity profile of the wood product into a lengthwise shrinkage map. One example of a lengthwise shrinkage map generated in this manner is shown in FIG. 4. This map can then be used to determine warp potential, such as crook, of the wood product. For example, the data comprising the lengthwise shrinkage map can be entered into a computerized finite element model (FEM) to be analyzed. The finite element model simulates the stress and strain components of the wood product. One such finite element model that my be utilized is the DIMENS model developed by Weyerhaeuser Company, Federal Way, Wash. The finite element model simulation quantitatively determines the warp potential for the wood product.
Thus, the prior art method includes the steps of: (1) measuring sound velocities at a plurality of measuring locations along a selected wood product, such as a Loblolly pine board, and compiling those measurements to form a sound velocity profile; (2) correlating sound velocity to lengthwise shrinkage from a plurality of specimens representative of the wood product; (3) converting the sound velocity profile into a lengthwise shrinkage map using the sound velocity-lengthwise shrinkage correlation; and (4) quantitatively determining the warp potential for the wood product by analyzing the lengthwise shrinkage map with a computerized finite element model, such as the DIMENS model. For a more detailed description of prior art warp potential determination methods, please refer to U.S. Pat. Nos. 6,293,152, 6,305,224 and 6,308,571, the disclosures of which are hereby incorporated by reference.
According to the aforementioned methods, warp-prone wood products can now be nondestructively identified during or prior to processing and product placement, resulting in more efficient processing of raw timber and lumber into wood products. Employing these methods may allow raw logs to be culled prior to manufacturing, and wood-products manufacturing processes to be altered to direct raw lumber to various end products according to quality and value. For example, warp-prone trees can now be identified while standing in forests or after cutting, and processed into products where warp is an irrelevant consideration (e.g. paper products, chipping, etc.). Green warp-prone lumber can be identified at the mill, separated, and kiln-dried using special warp-reducing techniques (e.g. rapid-drying, high-heat drying, final steaming, restraint-drying, etc.). Lumber having low warp potential can be dried using simpler and more economical methods.
Additionally, employing the currently known methods decreases the waste of natural resources by restricting the use of certain types of wood in inappropriate applications. For example, warp-prone logs determined by those methods can now be cut into lumber with cuts being coordinated to reduce warp, or the orientation of boards taken from certain logs can be altered to reduce warp. Alternatively, warp-prone logs can now be culled and processed for specific uses (e.g. chipped, lumber for pallets, etc.). Lumber cut from warp-prone logs also can be specially processed (e.g. special kiln drying techniques) or used in selected applications (e.g. relative constant moisture applications).
Further, warp-prone lumber can be identified for restrictive use in certain applications. For example, exterior window and door casings experience fluctuating moisture and temperature conditions during use. Warp prone lumber, even if initially straight when dried, could warp in such changing environments. Thus, the use of warp-prone lumber in warp-inducing environments can be avoided. Extremely warp-prone wood may be suitable only for uses where warping is not a significant problem (e.g. for pallets, landscape applications, etc.). In such cases, warp-prone green lumber can now be processed without expensive drying techniques.
While these currently known techniques for predicting warp potential in wood products have proven to be satisfactory in increasing the efficiency of lumber processing, improvements to these methods by the forest products industry are desired.